The disclosure is directed to vehicular stability control, and more particularly, to a method for enhancing vehicle stability control.
A vehicle stability control (VSC) system works by detecting when a driver has lost some degree of control. These systems are also known as ESP (electronic stability program) systems or VSE (vehicle stability enhancement) systems in the art. These systems automatically stabilize the vehicle to help the driver regain control. A central processor takes information from a number of sensors, and then determines whether the car is in a stable or unstable state. By combining the data from wheel speed sensors, steering angle sensors, yaw rate sensors (measuring the amount a vehicle rotates around its vertical center axis), and lateral acceleration sensors (measuring the amount of sideways acceleration generated by the vehicle), the central processing unit can actually detect when a vehicle is behaving in a way inconsistent with how the driver intends. If the processor does detect instability such as a slide produced by a sudden swerve, it automatically applies brake pressure to a select wheel (or wheels) to maintain or restore control.
ESP system safety analysis has identified that sensor faults, specifically faults of the yaw rate, lateral acceleration and hand wheel angle signals, require detection within a short period of time. One component integrated in the ESP system is an on-line sensor monitoring system that is mainly used for detecting faults in sensors as early as possible so the fail control system does not activate unnecessarily. Those faults, which cause the sensor output to exceed the operational range of the measured variable (for example, lateral acceleration significantly exceeding 10 m/s2) are relatively easy to detect and can typically be detected by the sensor circuit. Those faults resulting in erroneous sensor outputs, but still within the normal range of the measured signals, are more difficult to detect, and are the subject of this disclosure.
Current systems have a dynamic model based diagnostic strategy whose intent is to detect a failure of a sensor in the normal range for the measured signal. One available strategy performs sensor diagnostics only when the ESP system is active and does not activate failure detection when the vehicle is in the linear range of handling (that is during normal operation). If model based signal correlation discrepancy exists for more than several seconds after ESP goes active, a fault is declared. The first drawback with this strategy is that it is a reactive approach to a fault rather than a proactive one. If it is a sensor failure that caused an unwanted activation, this strategy can wait several seconds before declaring it a fault. The second drawback is that it can declare a false fault if the vehicle is in a true ESP maneuver for a prolonged period, even when there is no true fault (for example, in case of testing, demo, etc.). The third drawback is that it does not monitor sensor condition during normal driving.
Accordingly, there is a need for an ESP system capable to only use two of the three signals (steering angle sensors, yaw rate sensors and lateral acceleration sensors) in detecting a maneuver state, configured to detect even small deviations of the third missing signal successfully in steady state linear handling range of the vehicle. Additionally, there is a need for an ESP system able to selectively apply diagnostic thresholds based on the maneuver state and also if the vehicle is going straight or is in a turning maneuver. Furthermore, there is a need for an ESP system having the ability to isolate a fault successfully within a short period of time and not falsely call it a fault if the vehicle is truly in a quick transient or in a highly non-linear maneuver.